The present invention relates to turbomachine components and ceramic components made of silicon nitride. More specifically, the present invention relates to protective coatings for such components.
It is desirable to make certain gas turbine components of sintered silicon nitride ceramic. Silicon nitride blades, rotors and nozzles exhibit excellent mechanical and thermal properties, even when employed in flow streams at temperatures above 1200xc2x0 C. Moreover, the silicon nitride can counteract the adverse effects of oxidation and water vapor. Thus, turbine blades, rotors, and nozzles made partly or entirely of silicon nitride allow the gas turbines to operate at high temperatures.
It is also desirable to increase the gas turbine operating temperature beyond 1200xc2x0 C. Increasing the operating temperature would boost performance, improve efficiency and reduce pollutant emissions.
For operating temperatures approaching 1480xc2x0 C., however, even silicon nitride blades, rotors and nozzles can be adversely effected by oxidation and water vapor present in the flow stream. Oxidation can cause the silicon nitride to become brittle and fracture. Consequently, a component could fail.
Moreover, the silicon nitride components can be chipped or fractured by foreign objects such as carbon or metallic particles in the flow stream. Thus, impact by the foreign particles can also cause the components to fail.
It would be desirable to increase impact and oxidation resistance of silicon nitride components at operating temperatures beyond 1200xc2x0 C.
According to one aspect of the present invention, a component comprises a silicon nitride substrate; a porous silicon nitride matrix on the silicon nitride substrate, the porous silicon nitride matrix having a whisker-like morphology; and a noble metal infiltrated in the porous silicon nitride matrix.